The present invention relates to an improved photographic recording material for graphic arts prepress.
Photosensitive materials based on silver halide chemistry are used in a lot of applications, e.g. photographic materials for general amateur and professional photography in black-and white or color, recording and printing materials for the motion picture industry, and materials for the recording and duplication of medical diagnostic images. Further specific materials are developed for micrography, non-destructive testing and graphic arts pre-press. In graphic arts reproduction processes the original image appearing to have a continuous tone gradation is reproduced in a screening process by a collection of large number of dots, either by optical means in the case of a camera film or by electronic means in case of a recorder film. Apart from camera and recorder films there exist also so-called contact films which are able to duplicate screened images. In several photographic areas but in particular in graphic arts prepress films there is permanent need for lower manufacturing costs, higher covering power, sharper images, and reduced replenishment rates. This is especially the case for films with a great turnover such as a graphic arts recorder film which is designed for the recording of screened images, linework and text electronically stored in an image-setter or scanner.
It is an object of the present invention to provide a graphic arts recording film with improved covering power.
It is a further object of the present invention to provide a graphic arts recording film with lowered manufacturing costs.
The above mentioned objects are realized by providing a photographic recording material for graphic arts comprising a polyester support, subbed on both front and back sides with a latex subbing layer, and further comprising on the front side a gelatin subbing layer, one or more red sensitized emulsion layers having a total silver coverage of at most 3.6 g/m2 Ag (corresponding to 5.5 g/m2, expressed as AgNO3), and a total dry coverage of all other solid ingredients of at most 1.5 g/m2, and one or more anti-abrasive layers.
In a preferred embodiment the photographic recording material further comprises on the back side an antihalation layer comprising at most 1.5 g/m2 of gelatin and an antihalation dye.
The different elements of the invention will now be explained in detail.
The Emulsion Layer
The recording material of the present invention contains one or more emulsion layers, containing silver halide grains, a binder and other solid ingredients. In a most preferred embodiment of this invention there is just one emulsion layer. It is an essential feature of the present invention that the total silver coverage is at most 3.6 g/m2 Ag (corresponding to 5.5 g/m2 expressed as AgNO3). It is a further essential feature of the present invention that the total dry coverage of all other solid ingredients is at most 1.5 g/m2.
Graphic arts recording materials preferably use emulsions containing a majority of chloride, preferably between 50 mole % and 95 mole %, most preferably between 60 mole % and 89 mole %, and a low amount of iodide, the remaining halide being bromide.
The photographic emulsion(s) can be prepared from soluble silver salts and soluble halides according to different methods as described e.g. by P. Glafkidxc3xa8s in xe2x80x9cChimie et Physique Photographiquexe2x80x9d, Paul Montel, Paris (1967), by G. F. Duffin in xe2x80x9cPhotographic Emulsion Chemistryxe2x80x9d, The Focal Press, London (1966), and by V. L. Zelikman et al in xe2x80x9cMaking and Coating Photographic Emulsionxe2x80x9d, The Focal Press, London (1966). They can be prepared by mixing the halide and silver solutions in partially or fully controlled conditions of temperature, concentrations, sequence of addition, and rates of addition. The silver halide can be precipitated according to the single-jet method, the double-jet method, the conversion method or an alternation of these different methods.
The silver halide emulsions can be doped with various metal salts or complexes such as Rhodium and Iridium dopants.
The emulsion can be desalted in the usual ways e.g. by dialysis, by flocculation and re-dispersing, or by ultrafiltration.
The light-sensitive silver halide emulsions are preferably chemically sensitized as described e.g. in the above-mentioned xe2x80x9cChimie et Physique Photographiquexe2x80x9d by P. Glafkidxc3xa8s, in the above-mentioned xe2x80x9cPhotographic Emulsion Chemistryxe2x80x9d by G. F. Duffin, in the above-mentioned xe2x80x9cMaking and Coating Photographic Emulsionxe2x80x9d by V. L. Zelikman et al, and in xe2x80x9cDie Grundlagen der Photographischen Prozesse mit Silberhalogenidenxe2x80x9d edited by H. Frieser and published by Akademische Verlagsgesellschaft (1968). As described in said literature chemical sensitization can be carried out by effecting the ripening in the presence of small amounts of compounds containing sulphur e.g. thiosulphate, thiocyanate, thioureas, sulphites, mercapto compounds, and rhodamines. The emulsions can be sensitized also by means of gold-sulphur ripeners, gold-selenium ripeners or by means of reductors e.g. tin compounds as described in GB 739,823, amines, hydrazine derivatives, formamidine-sulphinic acids, and silane compounds. Chemical sensitization can also be performed with small amounts of Ir, Rh, Ru, Pb, Cd, Hg, Tl, Pd, Pt, or Au. One of these chemical sensitization methods or a combination thereof can be used.
The light-sensitive silver halide emulsions can be red sensitized with proper dyes such as those described by F. M. Hamer in xe2x80x9cThe Cyanine Dyes and Related Compoundsxe2x80x9d, 1964, John Wiley and Sons. Dyes that can be used for the purpose of spectral sensitization include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. Particularly valuable dyes are those belonging to the cyanine dyes, merocyanine dyes and complex merocyanine dyes. Specific patents on red sensitizers include U.S. Pat. No. 4,717,650, FR 2 058 405 and EP 427892.
The silver halide emulsion(s) for use in accordance with the present invention may comprise compounds preventing the formation of fog or stabilizing the photographic characteristics during the production or storage of photographic elements or during the photographic treatment thereof. Many known compounds can be added as fog-inhibiting agent or stabilizer to the silver halide emulsion. Suitable examples are disclosed in Research Disclosure Item 36544, September 1994, Chapter VII.
Besides the silver halide another essential component of a light-sensitive emulsion layer is the binder. The binder is a hydrophilic colloid, preferably gelatin. Gelatin can, however, be replaced in part or integrally by synthetic, semi-synthetic, or natural polymers.
The binders of the photographic element, especially when the binder used is gelatin, can be hardened with appropriate hardening agents such as those of the epoxide type, those of the ethylenimine type, those of the vinylsulfone type e.g. 1,3-vinylsulpohonyl-2-propanol, chromium salts e.g. chromium acetate and chromium alum, aldehydes e.g. formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds e.g. dimethylolurea and methyloldimethylhydantoin, dioxan derivatives e.g. 2,3-dihydroxy-dioxan, active vinyl compounds e.g. 1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds e.g. 2,4-dichloro-6-hydroxy-striazine, and mucohalogenic acids e.g. mucochloric acid and mucophenoxychloric acid. These hardeners can be used alone or in combination. The binders can also be hardened with fast-reacting. hardeners such as carbamoylpyridinium salts as disclosed in U.S. Pat. No. 4,063,952.
In a preferred embodiment of the present invention the emulsion layer further contains a polymeric latex functioning as plasticizer. A preferred latex is copoly(AMPS-butylmethacrylate), wherein AMPS means 2-acrylamido-2-methylpropane sulphonic acid, sodium salt, a monomer from Lubrizol Co. In a most preferred embodiment the latex is present in an amount of at least 15% by weight of all solids the silver halide grains excluded.
The photographic emulsion layer may further comprise various kinds of surface-active agents and lubricants in the photographic emulsion layer or in another hydrophilic colloid layer. Suitable surface-active agents and lubricants are disclosed in Research Disclosure Item 36544, September 1994, Chapter IX.
The Anti-abrasive Layer(s)
Usually in photographic materials there is only one anti-abrasive layer. on top of the emulsion layer. However, in a preferred embodiment of the present invention there are two thin anti-abrasive layers. In a still more preferred embodiment the anti-abrasive layer closest to the support contains a mixture of gelatin and a latex. In a most preferred embodiment this layer contains about 0.5 g/m2 of gelatin and about 0.5 g/m2 of latex. The latex uses may be the same as the latex optionally present in the emulsion layer. The top anti-abrasive layer is a gelatinous layer preferably withhout latex. Preferably its gelatin coverage is also about 0.5 g/m2. The anti-abrasive. layer may further contain spacing agents, wetting agents and lubricants, e.g. polyethylene dispersion.
The Latex Subbing Layers
The polyester support of the recorder film of the present invention is subbed on both sides with a so-called latex subbing layer. An essential ingredient of this latex subbing layer is an, adhesion promoting latex. A preferred class of latex polymers for this purpose are vinylidene chloride-containing copolymers having carboxyl functional groups. Illustrative of such polymers are (1) copolymers of vinylidene chloride and an unsaturated carboxylic acid such as acrylic or methacrylic acid, (2) copolymers of vinylidene chloride and a half ester of an unsaturated carboxylic acid such as the monomethylester of itaconic acid, (3) terpolymers of vinylidene chloride, itaconic acid and an alkyl acrylate or rethacrylate such as ethyl acrylate or methyl methacrylate, and (4) terpolymers of vinylidene chloride, acrylonitrile or methacrylonitrile and an unsaturated carboxylic acid such as acrylic acid or methacrylic acid.
In a most preferred embodiment the latex polymer is co(vinylidene chloride-methyl acrylate-itaconic acid 88%/10%/2%). This copolymer is prepared by emulsion polymerization using 0.5% MERSOLAT H (trade-mark of Bayer AG) as emulsifying agent. It is necessary to add extra surfactant, a so-called post-stabilizer, to the latex in order to assure a good stability on storage. An excellent storage stability is obtained when 4% of ULTRAVON W, trade mark of Ciba-Geigy, or DOWFAX, trade mark of Dow, is used.
As a further preferred ingredient of the coating solution of the latex subbing layer colloidal silica may be added as a binder. A preferred compound is KIESELSOL 100F (trade-mark of Bayer AG), average particle size 25-30 nm. The ratio of the amount of latex to silica is preferably about 80/20.
The dry thickness of the latex subbing layer is preferably about 0.1 mm.
The latex subbing layer of the back side is preferably of similar composition as the latex subbing layer on the upper side. However, in a particularly preferred embodiment this layer further contains a conductive polymer in order to make the layer antistatic. The nature of this conductive compound will now be explained in detail.
Such a compound, usually a polymer, can show ionic or electronic conductivity. The conductivity however of an antistatic layer containing ionic conductive polymers, even after cross-linking, is moisture dependent. Therefore electronically-conducting conjugated polymers have been developed. Substances having electronic conductivity instead of ionic conductivity have a conductivity independent from moisture. They are particularly suited or use in the production of antistatic layers with permanent and r producible conductivity.
Many of the known electronically conductive polymers are highly colored which makes them less suited for use in photographic materials, but some of them of the group of the polyarenemethylidenes, e.g. polythiophenes and polyisothianaphthene are not prohibitively colored and transparent, at least when coated in thin layers. As a result polythiophene derivatives are a preferred type of conductive compounds for use in the present invention.
The production of conductive polythiophenes is described in preparation literature mentioned in the above mentioned book: xe2x80x9cScience and Applications of Conducting Polymersxe2x80x9d, p. 92.
For ecological reasons the coating of antistatic layers should proceed where possible from aqueous solutions by using as few as possible organic solvents. The production of antistatic coatings from aqueous coating compositions being dispersions of polythiophenes in the presence of polyanions is described in EP 0 440 957. Thanks to the presence of the polyanion the polythiophene compound is kept in dispersion.
Preferably said polythiophene has thiophene nuclei substituted with at least one alkoxy group, or xe2x80x94O(CH2CH2O)nCH3 group, n being 1 to 4, or, most preferably, thiophene nuclei that are ring closed over two oxygen atoms with an alkylene group including such group in substituted form.
Preferred polythiophenes for use according to the present invention are made up of structural units corresponding to the following general formula: 
in which:
each of R1 and R2 independently represents hydrogen or a C1-4 alkyl group or together represent an optionally substituted C1-4 alkylene group or a cycloalkylene group, preferably an ethylene group, an optionally alkyl-substituted methylene group, an optionally C1-12 alkylxe2x80x94or phenyl-substituted 1,2-ethylene group, a 1,3-propylene group or a 1,2-cyclohexylene group.
The most preferred compound is poly(3,4-ethylenedioxy-thiophene), (PEDT) with following formula: 
The preparation of said polythiophene and of aqueous polythiophene-polymeric polyanion dispersions containing said polythiophene is described in EP 0 440 957, cited above.
Suitable polymeric polyanion compounds required for keeping said polythiophenes in dispersion are provided by acidic polymers in free acid or neutralized form. The acidic polymers are preferably polymeric sulphonic acids. Examples of such polymeric acids are polymers containing vinyl sulfonic acid and styrene sulfonic acid or mixtures thereof.
The anionic acidic polymers used in conjunction with the dispersed polythiophene polymer have preferably a content of anionic groups of more than 2% by weight with respect to said polymer compounds to ensure sufficient stability of the dispersion. Suitable acidic polymers or corresponding salts are described e.g. in DE-A -25 41 230, DE-A-25 41 274, DE-A-28 35 856, EP-A-14 921, EP-A-69 671, EP-A-130 115, U.S. Pat. No. 4,147,550, U.S. Pat. No. 4,388,403 and U.S. Pat. No. 5,006,451.
The weight ratio of polythiophene polymer to polymeric polyanion compound(s) can vary widely, for example from about 50/50 to 15/85.
The most preferred polymeric polyanion for use in combination with the polythiophene derivative, e.g. PEDT, is polystyrene sulphonate (PSS).
The conductive latex subbing layer has preferably a dry thickness of about 0.1 mm.
The Gelatin Subbing Layer
The gelatin subbing layer is coated on top of the the latex subbing layer on the front side. Apart from the spacing agent the gelatin subbing layer preferably contains a mixture of gelatin and colloidal silica. A preferred compound is again KIESELSOL 300F (trade-mark of Bayer AG). A plasticizing compound can be used in order to avoid the formation of cracks in the dried layer due to the occurence of excessive shrinking of the layer during drying. Plasticizing agents are well-known in the art. Low-molecular weight compounds (e.g. acetamide, glycerin) as well as polymeric latices (e.g. polyethylacrylate, poly-n.-butylacrylate) can be used for this purpose. Furtheron the gelatin subbing layer may contain one or more surfactants. Useful surfactants include: ULTRAVON(trademark) W, an aryl sulfonate from CIBA-GEIGY, DOWFAX from Dow CO., and ARKOPAL(trademark) N060 (previously HOSTAPAL(trademark) W), a nonylphenylpolyethylene-glycol from HOECHST.
The thickness of the gelatin subbing layer is preferably comprised between 0.1 and 1 xcexcm.
The Antihalation Layer
In a most preferred embodiment of the present invention an antihalation layer is present on the back side of the support on top of the latex subbing layer. An antihalation layer contains an antihalation dye and a binder. Antihalation dyes improve the image sharpness by diminishing the upward reflection of light by the support into the emulsion layer. Useful dyes absorbing in the visible spectral region include the colored piments of U.S. Pat. No. 2,697,037, the pyrazonol oxonol dyes of U.S. Pat. No. 2,274,782, the styryl and butadienyl dyes of U.S. Pat. No. 3,432,207, the diaryl azo dyes of U.S. Pat. No. 2,956,879, the merocyanine dyes of U.S. Pat. No. 2,527,583, the merocyanine and oxonol dyes of U.S. Pat. No. 3,486,897, U.S. Pat. No. 3,652,284 and U.S. Pat. No. 3,718,472, and the enaminohemioxonol dyes of U.S. Pat. No. 3,976,661. Dyes absorbing in the red spectral region of the di- or triphenylmethane type, some of which bear an electron-withdrawing group, are disclosed in e.g. U.S. Pat. No. 2,282,890, DE 1038395, FR 2,234,585, JP-A 59-228250, U.S. Pat. No. 2,252,052 and A. Guyot, Compt. Rend., Vol 114 (1970), p.1120. Some of the compounds disclosed contain one or more water-solubilizing groups.
It can be advantageous that the antihalation dye is non-diffusible under normal coating conditions and only becomes diffusible and/or discolors under alkaline processing conditions. Such dyes can be incorporated as dispersions or as so-called microcrystalline solid particles. Non-diffusible or hardly diffusible dyes of this type are described in e.g. U.S. Pat. No. 4,092,168, EP 274723, EP 276566, EP 294461, EP 299435, GB 1563809, EP 015601, U.S. Pat. No. 4,857,446, JP-A 02-259752, JP-A 02-264247, EP 582753, EP 587229.
It is an essential feature of the present invention that the antihalation layer is a thin layer having a gelatin coverage of at most 1.5 g/m2.
Coating Technology
In a particularly preferred embodiment the two latex subbing layers, the gelatin subbing layer, and the antihalation layer are coated xe2x80x9con linexe2x80x9d in a continuous process in the manufacturing alley of the polyester itself. Molten polyester is extruded and longitudinally stretched. Then the first latex subbing layer is applied on the upper side and the second latex subbing layer, optionally conductive, is applied on the back side. Then the subbed polyester is stretched in the transversal direction. The gelatin subbing layer is applied on the upper side, and finally the antihalation layer is applied on the back side.
The emulsion layer(s) and the anti-abrasive layers are coated xe2x80x9coff-linexe2x80x9d. Any well-known coating technique can be used such as dip coating, air-knife coating, slide hopper coating, and curtain coating. In a preferred embodiment the emulsion layer and the two anti-abrasive layers are applied by curtain coating.